This invention pertains to sensing when inspiration takes place during breathing cycles of air-breathing animals, including humans, that triggers a dose of therapeutic gas to be inhaled when inhalation begins, with the dose of therapeutic gas determined by the length of the previous breath, which results in automatic adjustment of the therapeutic dose to the rate of breathing of the air-breathing animal, including humans.
In this invention the sensing of inhalation and delivery of the therapeutic gas is accomplished by making a single connection between the respiratory apparatus and the air-breathing animal, including humans. This single connection can be a nasal cannula (of the type normally used for delivering oxygen therapy) or a similar device that must be relied upon both for sensing the length of breath and for delivering the triggered dose of therapeutic gas. This dual function cannot be carried on simultaneously for the dose must be terminated before the end of the breathing cycle and the length of the dose of gas must be determined from the previous breath for it is impossible to establish what the length of the next breath will be until it occurs.
A problem occurs when the previous breath is extremely long, which happens when the "sigh mechanism" takes place, which is an unusually large breath that takes place periodically.
When this occurs, the next dose, that is determined by the last breath, would be so large that the nasal cannula would not be able to sense when the next short breath takes place, because the nasal cannula would be giving a dose of therapeutic gas that is longer than the next breath.
To overcome this problem, the maximum dose of therapeutic gas is limited to 2 seconds. Thus, the maximum dose is used to trigger the next dose after a "sigh breath" occurs. Since, in this invention, the maximum adjustable dose is 50% of the previous dose, the new dose after a "sigh breath" would be a maximum of one second.
The maximum rate of breathing that can be detected after a "sigh breath" is 60 breaths per minute. Since the most rapid rate of breathing is by infants, approximately 40 breaths per minute maximum, the limiting of the dose to 2 seconds overcomes the problem created by the "sigh breaths" that periodically occur. The rate of breathing for an adult is 15 to 20 breaths per minute, and for babies 20 to 40 breaths per minute; all less than the 60 breaths per minute limitation of this invention.
In this invention the length of the dose can be adjusted as a percentage of the last breath.
In prior art, the dose is either set as a fixed length of time that is manually set, or by detecting when inhalation takes place, and terminating the dose when exhalation takes place.
If a single nasal cannula is used, it is impossible for a sensor to have the dual function of sensing and delivering the dose, as only one function at a time can take place.
The prior art taught in Greenwood, Pat. No. 4,744,356 (May 17, 1988) illustrates the requirement for a separate sensor to detect the inhalation and a nasal cannula to deliver the therapeutic gas. It lacks the feature of selecting the length of the dose as a percentage of the length of breath, for it is impossible for the Greenwood device to determine what the length of the next breath will be before it takes place.
The J. E. Finan U.S. Pat. No. 3,400,713 (Sept. 10, 1968) is similiar in operation to Greenwood, the only difference being that one employs electronic detection and the other mechanical detection.
The prior art taught in the Durkan Pat. No. 4,414,982 (Nov. 15, 1983) illustrates the use of a fixed adjustable time to manually regulate the length of the dose and requires a dual nasal cannula where one nostril is used for sensing, and the other nostril for delivering the therapeutic gas. The Durkan invention does not have the feature of automatic adjustment of the therapeutic dose to the rate of breathing and must be manually adjusted.
The invention described in this specification teaches a method for automatic adjustment of the therapeutic dose to the rate of breathing, the apparatus required, and the special combination of components necessary to accomplish this automatic adjustment.